1. Field of the Invention
The present invention relates to direction-finding systems and directional locating devices, and more particularly to transmitter and receiver apparatus for determining the relative direction to a remote source from which radio transmissions radiate from the transmitter and are detected by the receiver.
While the invention has particular application to the sport of hunting where a dog seeks to locate game such as birds, coon or bear, the transmitter and receiver circuitry of the invention can be utilized in other applications such as, for example, locating children in the woods by attaching the transmitter to a child's belt, or military use for locating, for example, parachutists, after a jump for the purpose of regrouping. The invention has generic application to the location of a moving object carrying a signal-generating transmitter by detecting the radiated transmitted signals with a receiver having directional-sensing capabilities.
2. Prior Art
U.S. Pat. No. 3,336,530, "Direction Finding System for Hunting Dogs", utilizes a miniaturized transmitter carried by a hound dog and an omni-directional antenna mounted on the dog's collar. A miniaturized receiver carried by the hunter includes a highly directional antenna, such as a loop antenna, as illustrated in FIG. 5 of the patent. However, this patent does not disclose details of the demodulator circuitry in the receiver and does not utilize, in combination, both a loop antenna and a "sense" antenna as does the subject invention.
U.S. Pat. No. 3,790,948 discloses a radio transmitter located in the head of a hunting arrow to enable a hunter to locate the arrow and/or the animal in which the arrow is embedded.
U.S. Pat. No. 3,626,416 discloses a direction finding receiver worn by an individual to determine the direction of a transmitted signal. The system incorporates a binaural receiver which converts the radio frequency signal received by the two antennas into a pair of audio frequency signals such that the phase relationship between the received radio frequency signals is preserved.